Search results for "ASTROPHYSICS"
showing 10 items of 8341 documents
Flares from small to large: X-ray spectroscopy of Proxima Centauri with XMM-Newton
2003
(Abridged) We report results from a comprehensive study of the nearby M dwarf Proxima Centauri with the XMM-Newton satellite. We find strongly variable coronal X-ray emission, with flares ranging over a factor of 100 in peak flux. The low-level emission is found to be continuously variable. Several weak flares are characteristically preceded by an optical burst, compatible with predictions from standard solar flare models. We propose that the U band bursts are proxies for the elusive stellar non-thermal hard X-ray bursts suggested from solar observations. A very large X-ray flare was observed in its entirety, with a peak luminosity of 3.9E28 erg/s [0.15-10 keV] and a total X-ray energy of 1…
GJ 357 b: A Super-Earth Orbiting an Extremely Inactive Host Star
2020
Aims. In this paper we present a deep X-ray observation of the nearby M dwarf GJ 357 and use it to put constraints on the atmospheric evolution of its planet, GJ 357 b. We also analyse the systematic errors in the stellar parameters of GJ 357 in order to see how they affect the perceived planetary properties. Methods. By comparing the observed X-ray luminosity of its host star, we estimate the age of GJ 357 b as derived from a recent XMM-Newton observation (log Lx [erg s-1] = 25.73), with Lx-age relations for M dwarfs. We find that GJ 357 presents one of the lowest X-ray activity levels ever measured for an M dwarf, and we put a lower limit on its age of 5 Gyr. Using this age limit, we perf…
ARES. III. Unveiling the Two Faces of KELT-7 b with HST WFC3
2020
We present the analysis of the hot-Jupiter KELT-7b using transmission and emission spectroscopy from the Hubble Space Telescope (HST), both taken with the Wide Field Camera 3 (WFC3). Our study uncovers a rich transmission spectrum which is consistent with a cloud-free atmosphere and suggests the presence of H2O and H-. In contrast, the extracted emission spectrum does not contain strong absorption features and, although it is not consistent with a simple blackbody, it can be explained by a varying temperature-pressure profile, collision induced absorption (CIA) and H-. KELT-7 b had also been studied with other space-based instruments and we explore the effects of introducing these additiona…
Oscillations on Width and Intensity of Slender Ca ii H Fibrils from Sunrise/SuFI
2017
R. Gafeira et. al.
P and S wave travel time tomography of the SE Asia-Australia collision zone
2019
© 2019 Elsevier B.V. The southeast (SE)Asia - Australia collision zone is one of the most tectonically active and seismogenic regions in the world. Here, we present new 3-D P- and S-wave velocity models of the crust and upper mantle by applying regional earthquake travel-time tomography to global catalogue data. We first re-locate earthquakes provided by the standard ISC-Reviewed and ISC-EHB catalogues using a non-linear oct-tree scheme. A machine learning algorithm that clusters earthquakes depending on their spatiotemporal density was then applied to significantly improve the consistency of travel-time picks. We used the Fast Marching Tomography software package to retrieve 3-D velocity a…
A Search for IceCube Events in the Direction of ANITA Neutrino Candidates
2020
During the first three flights of the Antarctic Impulsive Transient Antenna (ANITA) experiment, the collaboration detected several neutrino candidates. Two of these candidate events were consistent with an ultra-high-energy up-going air shower and compatible with a tau neutrino interpretation. A third neutrino candidate event was detected in a search for Askaryan radiation in the Antarctic ice, although it is also consistent with the background expectation. The inferred emergence angle of the first two events is in tension with IceCube and ANITA limits on isotropic cosmogenic neutrino fluxes. Here, we test the hypothesis that these events are astrophysical in origin, possibly caused by a po…
Spectropolarimetric evidence for a siphon flow along an emerging magnetic flux tube
2016
©2017 The American Astronomical Society. All rights reserved.We study the dynamics and topology of an emerging magnetic flux concentration using high spatial resolution spectropolarimetric data acquired with the Imaging Magnetograph eXperiment on board the sunrise balloon-borne solar observatory. We obtain the full vector magnetic field and the line of sight (LOS) velocity through inversions of the Fe i line at 525.02 nm with the SPINOR code. The derived vector magnetic field is used to trace magnetic field lines. Two magnetic flux concentrations with different polarities and LOS velocities are found to be connected by a group of arch-shaped magnetic field lines. The positive polarity footp…
The GAPS Programme with HARPS-N at TNG: . Atmospheric Rossiter-McLaughlin effect and improved parameters of KELT-9b
2019
In the framework of the GAPS project, we observed the planet-hosting star KELT-9 (A-type star, VsinI$\sim$110 km/s) with the HARPS-N spectrograph at the TNG. In this work we analyse the spectra and the extracted radial velocities (RVs), to constrain the physical parameters of the system and to detect the planetary atmosphere of KELT-9b. We extracted from the high-resolution optical spectra the mean stellar line profiles with an analysis based on the Least Square Deconvolution technique. Then, we computed the stellar RVs with a method optimized for fast rotators, by fitting the mean stellar line profile with a purely rotational profile instead of using a Gaussian function. The new spectra an…
Titan's surface albedo variations over a Titan season from near-infrared CFHT/FTS spectra
2006
International audience; We have observed Titan in a series of campaigns from 1991 to 1996 with the Fourier Transform Spectrometer on the CFH telescope. The data acquired provide a lightcurve from the geometric albedos in the 0.9–View the MathML source spectral region. The 1991–1993 data were previously analyzed in Coustenis et al. [1995. Titan's surface: composition and variability from its near-infrared albedo. Icarus 118, 87–104] with a spherical particle code by McKay et al. [1989. The thermal structure of Titan's atmosphere. Icarus 80, 23–53]. We present here three new datasets from the 1994, 1995 and 1996 observations, with additional information from the 0.94-μm methane window on Tita…
Stage–Discharge Relationship for an Upstream Inclined Grid with Transversal Bars
2016
AbstractCheck dams with grids upgrading upstream are often used in mountain rivers, where intense sediment transport and steep slopes occur. In some cases, sloping grids are used in the construction of debris flow breakers. In this paper, the outflow process of an upstream-inclined grid with transversal bars is studied by using the dimensional analysis and the incomplete self-similarity theory. Next, the theoretical analysis shows that a power equation can be used for establishing the stage-discharge equation. The coefficient of the power equation depends on both the slope angle and the void ratio, whereas the exponent depends only on the slope angle. Finally, this deduced stage–discharge r…